A conventional television system, such as a system in accordance with the NTSC broadcast standard adopted in the United States and elsewhere, processes a television signal representative of an image with a standard 4:3 aspect ratio (the ratio of the width to the height of a displayed image). Recently, there has been interest in using wider aspect ratio images for television systems, such as 5:3, 16:9 and 2:1, since these wider aspect ratios more nearly approximate or equal the aspect ratio of the human eye compared to the 4:3 aspect ratio of a standard television display.
Compatible advanced television systems for producing wide aspect ratio images are described, for example, in U.S. Pat. No. 4,816,899--Strolle et al., in U.S. Pat. No. 4,855,811--Isnardi, and in (allowed) co-pending U.S. patent application Ser. No. 509,384, U.S. Pat. No. 5,053,858 issued Oct. 1991) of J. L. Koslov et al. titled "Chrominance Signal Processing Apparatus for a Widescreen Television System". In these systems certain baseband side panel information is encoded by time expansion and amplitude modulation of a field phase modulated auxiliary subcarrier of a type sometimes referred to as a Fukinuki carrier. A Fukinuki carrier is related to a standard interlaced carrier such as the NTSC color subcarrier, but is located in different quadrants of the vertical-temporal frequency spectrum. Such an auxiliary carrier can be generated by inverting the phase of an interlaced carrier on alternate image fields. In the system described by Koslov et al., center panel "I" and "Q" color difference signal image information respectively amplitude modulates in-phase and quadrature phased standard 3.58 MHz color subcarrier components. In addition, quadrature phased Fukinuki-type auxiliary subcarrier components also at 3.58 MHz are amplitude modulated by side panel "I" color difference information (the inphase component), and by side panel "Q" color difference information together with high frequency side panel luminance information (the quadrature component). A system of this type is also described in a report submitted by the David Sarnoff Research Center, Princeton, N.J., to the Federal Communications Commission in the United States, titled "System Description, Advanced Compatible Television", dated Dec. 31, 1989.
A field phase and amplitude modulated Fukinuki-type carrier generates complementary color flicker which typically is not visible because of the complementary colors involved, and because in theory luminance information is not involved. However, it is herein recognized that, in practice, nonlinearities associated with display devices (e.g., kinescopes, among others) convert otherwise imperceptible chrominance flicker into visible luminance flicker. More specifically, practical display devices such as kinescopes typically exhibit a nonlinear transfer characteristic in the active region above black level to white level, even if an inherent nonlinear transfer characteristic in this region is attempted to be corrected at the transmitter via a so-called "gamma correction" of the television signal. This result occurs due to dissimilarities among display devices, and to signal processing effects. Another source of non-linearity in a display device is the region below black level in which the display device is cut-off.
Luminance flicker associated with a Fukinuki-type modulated carrier therefore can result from display device nonlinearities in the active region. Such luminance flicker also can result from carrier modulation excursions into the cut-off region. Noticeable luminance flicker can occur when the center panel and the side panels contain highly saturated colors, e.g., when the center and side panels exhibited similar saturated colors such as blue (sky) or green (grass). Uniform saturated blue color was found to cause very visible flicker, partly because saturated blue color exhibits a low luminance level. The described luminance flicker problem is addressed by the present invention, which significantly reduces or eliminates such luminance flicker.